Different style of Langmuir isotherm model of non-competitive sorption Zn(II) and Cd(II) onto horse dung humic acid (HD-HA)

The objective of this work was to investigate the best style of Langmuir isotherm model of Non-Competitive Sorption Zn(II) and Cd(II) on Horse Dung Humic Acid (HD-HA). The sorbent (HD-HA) was extracted by Stevenson’s method and it was characterized by FT-IR, UV-Vis, and total of acidity. The sorbent was applied to sorbed Zn(II) and Cd(II) in optimum pH and separated container. The data was then analyze by four style of Langmuir isotherm model i.e. Langmuir-a, Langmuir-b, Langmuir-c, and Langmuir-d. The result of characterization study by FT-IR, UV-Vis, and content of acidity was the HD-HA has the very similar character with PS-HA. It was proved in this work by separation factor (RL) that all of the style was favorable, but the most used Langmuir style in some publication, Langmuir-a, have the best linearity in both Cd(II) and Zn(II) sorption. Selection of usage of these style has no significant difference to determine the sorption capacity (b), but it has broad values to equilibrium constant (KL) which in this study ranged 5651-10000 L/mole and 7929-11111 L/mole for Cd(II) and Zn(II), respectively. The best linearity of application the sorption in kinetics equation was follow pseudo-second order Ho kinetics equation. The relationship of RBS kinetics equation with Langmuir data was the value of K from ka/kd of RBS equation which was 3452 (L/mole) for Cd(II) and 10898 (L/mole) for Zn(II). The value of KL and K of Zn(II) sorption was nearly close and value of K from RBS kinetics equation is in the range of KL from different Langmuir style. The value of K of Cd(II) sorption was not so close and out of range of different style Langmuir data.